When it comes to doujins its mostly the cleaning the pages up. The translators I know can get any doujin done in 5minute fully translated.
When it comes to anime part of the wait depends. Cleaning up after can take hours depending on your staff skill or it cant take a few minutes. Depends on each persons skills, mostly grammar. Translation can take hours for new Translators but the experienced ones can get them done pretty fast.
Translation is general, From what I know theres two kinds of translation, Literal and one that is from ideas. Whichever is better is debatable has people have different opinions. J > E doesn't work just word by word even with grammar fixes. There is an art to it I am told. Different translators will give you different answers.
Note I don't speak Japanese or do translations. I just do fansubbing so I know at least something about J > E Translation.